Mussel and plant cell wall-inspired soy protein adhesives: High strength, flame retardancy, and mildew resistance.

Traditional soybean adhesives lack water resistance and are prone to microbial attack. Inspired by mussel adhesion and plant cell wall chemistry, we engineered a high-performance soybean-based adhesive with robust water and mildew resistance. The adhesive is equipped with a multiscale bonding network that is composed of tannic acid (TA) that has been depolymerised and grafted with epoxy compounds (E-DTA), borax (B), and soybean meal (SM). The adhesive's overall performance was improved by the construction of a highly cohesive cross-linked framework through the formation of imine bonds (Schiff base, CN) and CN covalent cross-linking between the catechol/epoxy groups of E-DTA and SM molecules. Through synergistic coordination between borax and the SM/E-DTA matrix, a dynamic cross-linking network was further established. This network included dynamic boronate ester bonds (B-O-C) and nitrogen‑boron coordination bonds (NB). Through the process of reversible bond dissociation and reconfiguration, this structure effectively absorbs mechanical stress, thereby providing the adhesive with exceptional durability. The bio-based adhesive demonstrated substantial improvements in moist shear strength and fracture toughness when contrasted with pure SM. Specifically, the bio-based adhesive improved by 182.2 % (1.37 MPa) and 484.5 % (0.9 J). Furthermore, the adhesive exhibited exceptional flame retardancy (LOI 31.6 %), mildew resistance, and economic efficacy and sustainability, which offers new insights for the development of SM-based adhesives.